The present invention relates to a pattern forming process used in production of semiconductor elements, etc. More particularly, the present invention relates to a pattern forming process used for pattern formation employing ultraviolet rays of 450 nm or less, particularly i-line of 365 nm as an energy source for exposure.
It has been reported to apply conventional chemical amplification type resists to deep ultraviolet rays (e.g. of excimer laser), X-rays and electron-beam lithography, and good results have been obtained. Their application to i-line which has a short wavelength and is promising for formation of fine pattern, was also considered; however, it has been seldom tried because conventional chemical amplification type resists have little absorption for i-line and have been presumed to have no sensitivity to i-line. Under such circumstances, the present inventors exposed chemical amplification type resists to i-line and confirmed that chemical amplification type resists are effective also in an i-line region. In FIG. 8 is shown an example of the pattern forming process using a conventional chemical amplification type resist. A conventional chemical amplification type resist 6 is spin coated on a semiconductor silicon substrate 1, and then is soft baked on a hot plate 3 at 90.degree. C. for 90 sec to obtain a pattern forming film of 1.28 .mu.m in thickness [FIG. 8A]. Next, an i-line 4 is applied through a mask 5 [FIG. 8B]. Baking is effected on the hot plate 3 at 110.degree. C. for 90 sec [FIG. 8C]. Thereafter, development with tetramethylammonium hydroxide (TMAH) is effected for 60 seconds to dissolve the exposed portions 6A of the conventional pattern forming material 6 to obtain a positive type pattern 6B [FIG. 8D]. However, conventional chemical amplification type resists show little absorption to i-line as mentioned above; accordingly, they are easily affected by the reflection from the substrate as shown in FIG. 8B to form a pattern of reversed taper shape as shown in FIG. 8D; as a result, they have been unable to provide a fully satisfactory pattern.
As mentioned above, the present inventors confirmed that conventional chemical amplification type resists are effective also in an i-line region. However, showing little absorption to i-line, these resists are easily affected by the reflection from the substrate and form a pattern of reversed taper shape.